The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode, coupled thereto and positioned at a pacing site, either endocardial or epicardial. Mechanical complications and/or MRI compatibility issues, which are sometimes associated with elongate lead wires and well known to those skilled in the art, have motivated the development of implantable cardiac pacing devices that are wholly contained within a relatively compact package for implant in close proximity to the pacing site, for example, within the right ventricle RV of the heart. With reference to FIG. 1, such a device 100 is illustrated, wherein an hermetically sealed housing 105, preferably formed from a biocompatible and biostable metal such as titanium, contains a pulse generator, or an electronic controller and associated power source (not shown), to which at least one electrode 111 is coupled, for example, by a hermetic feedthrough assembly (not shown) like those known to those skilled in the art. Housing 105 may be overlaid with an insulative layer, for example, medical grade polyurethane, parylene, or silicone, and a portion of the insulation layer may be removed to form another electrode 112, for example, which provides bipolar pacing and sensing in conjunction with electrode 111.
FIG. 1 shows device 100 having been deployed by an operator out from a distal opening 803 of a delivery catheter 800, which the operator has maneuvered up through the inferior vena cava IVC and the right atrium RA into the right ventricle RV. The deployed device 100 is shown fixed at an implant site by a fixation member 115 thereof, but still secured to catheter 800 by a tether 880 that extends out from distal opening 803 of catheter 800.
Securing device 100 to catheter 800 with tether 880 is typically accomplished, prior to maneuvering catheter 800, with device 100 loaded therein, to the illustrated site, by looping tether 880 through a tethering feature 121 of device 100 and threading first and second lengths 881, 882 of tether 880 through one or more lumens of catheter 800 such that opposing ends thereof protrude out from a proximal opening 801 of catheter 800. After deploying device 100, the operator can grasp the ends of lengths 881, 882, for example, to tug on tether 880 to test the fixation of device 100 at the implant site, and/or to apply a greater force to tether 880 to remove device 100 from the implant site for repositioning at a more suitable site, if necessary. If satisfied with the implant of device 100, the operator can remove the looped tether 880 from engagement with device 100 by releasing, for example, the end of length 881, and then pulling on the end of the other length 882, thereby withdrawing an entirety of length 882 proximally through delivery catheter 800 so that the other length 881 is pulled distally and through device tether tethering feature 121, out from engagement therewith.